Conventional bicycles are propelled by rotary motion. Foot pedals are mounted to crank arms that rotate on the bicycle frame. The crank arms in turn rotate a large central drive sprocket coupled by an endless chain to a rear wheel sprocket. As the rider moves the pedals in circles, the rear wheel rotates in a forward angular direction, propelling the bicycle. A bicycle may be easier to operate if a rider were able simply to step up and down on pedals.
The prior art has proposed numerous bicycles and similar vehicles that operate in response to stepping motion, sometimes referred to in the prior art as rectilinear or reciprocating motion. One example is to be found in U.S. Pat. No. 1,332,185 to Brown which describes a stepper tricycle with a drive mechanism that includes a pair of ratchet wheels mounted on a rear axle. A pair of elongate pedals, pivoted to a forward section of the tricycle frame, carry blade-like pawls that mesh with the ratchet wheels. Each pedal thus applies a propelling torque to the axle as the pedal descends under the user's weight, and a biasing spring restores the pedal to a raised position afterwards.
U.S. Pat. No. 1,601,249 to Hayden describes a stepper cycle that has two pedals pivoted to the front of its frame. Once again, there is no central drive sprocket, rear wheel sprocket and endless chain. Instead, each pedal carries a near-vertical, toothed track that is meshed with a pinion mounted on a rear axle. Each pedal consequently delivers a torque to the rear axle and ultimately to a rear wheel, which is mounted by clutches to the rear axle, whenever the user steps on the pedal. Springs restore the pedals to an upper position after each step.
U.S. Pat. No. 2,449,266 to Woods describes a stepper cycle which has two elongate pivoting pedals. The pedals are coupled to the axle on which rear wheels are mounted. Each pedal is associated with a linkage that pulls a short length of chain, wrapped around a sprocket, as the pedal descends. The sprocket is mounted on the exterior of a clutch mechanism adapted to rotate the axle. A spring mechanism is used to restore each pedal to an upper position.
U.S. Pat. No. 3,913,945 to Clark discloses a stepper bicycle that more closely resembles a conventional bicycle but, once again, has no central drive sprocket. Two curved pedals are pivoted to a forward section of the cycle and carry conventional cycle-like pedals. Downward displacement of a pedal causes a chain to be drawn around a sprocket coupled to the rear wheel, propelling the bicycle. Two springs compress as the pedals pivot downward and serve to restore the pedals to their starting positions.
U.S. Pat. No. 5,335,927 to Islas discloses another bicycle propelled by stepping action. Two pedals are pivoted to rear sections of the bicycle frame and extend forward to support pedals. An elaborate system of pulleys, sprockets, and chain couples the pedals to the rear wheel.
U.S. Pat. No. 5,716,069 to Bezerra et al describes a compact mechanism which in essence replaces the conventional pedals and central drive sprocket associated with a bicycle, allowing stepping action on pedals to be converted into torque. The mechanism includes a housing that contains one shaft about which two pedal levers pivot and another shaft that supports a large drive sprocket at one side of the mechanism. A combination of clutch assemblies, pinions, and toothed racks, all compactly mounted in the housing, enables the drive sprocket to rotate in response to stepping action on the pedals. The drive sprocket is coupled to the rear wheel of the bicycle via a sprocket coaxial with the rear wheel and an endless chain coupling the sprockets.
U.S. Pat. No. 5,871,221 to Min et al describes a drive mechanism for a stepper-type bicycle that locates where the large central drive sprocket of a conventional bicycle is normally positioned. The mechanism includes a transverse drive shaft bearing mounted for rotation within a horizontal drum. Right and left pedal arms are mounted to opposite ends of the drive shafts and cause a length of drive chain to be drawn over a conventional rear wheel sprocket. An upper end of the chain is fixed to one “pulling rod” and a lower end, to another. The pulling rods cooperate to pull the upper length of chain forward, rotating the rear wheel sprocket.
U.S. Pat. No. 6,334,838 to Lee describes an exercise cart that has a mechanism for powering its rear wheels in response to a rider's stepping action. The mechanism uses a pair of gears that are bearing mounted on a common rod to either side of a drive sprocket. Two pivoting pedals are provided, and each carries on its underside a curved driving element formed with transverse teeth, that meshes with one of the gears. An endless chain couples the drive sprocket and a rear wheel sprocket. When either pedal is depressed, the associated gear is rotated, which in turn rotates the drive sprocket and ultimately the cart's rear wheels. The patent proposes using two hydraulic cylinders as springs to restore the pedals to their uppermost position.
U.S. Pat. No. 6,334,838 to Kugel et al discloses a stepper bicycle with a central drive sprocket coupled to a rear wheel sprocket with an endless chain, as in a conventional bicycle. Drive mechanisms are located on either side of the drive sprocket. Each mechanism includes an elongate housing with a U-shaped cross-section, and a fiat rectangular gear that slides in the housing and has gear teeth along one side edge. The housing has a vertical slot through which a pedal is attached to the sliding rectangular gear. A “quadrant” gear is fixed to the shaft supporting the drive sprocket. The quadrant gear has a part-circular peripheral edge which has gear teeth meshed with those of the sliding rectangular gear. Thus, as the rectangular gear is forced downward, the drive sprocket is rotated in a forward angular direction. Tops of the sliding rectangular gears of the two drive mechanisms are coupled by a cable that runs over two overhead pulleys so that, as one is forced downward by foot, the other gear (decoupled by a clutch mechanism) is raised in preparation for another power stroke.
U.S. Pat. No. 6,648,355 to Ridenhour discloses yet another stepper bicycle. Two pedals are mounted on arms hinged to a forward part of the bicycle frame. A D-shaped bracket (quadrant member) is attached to the pedal bracket. One end of a length of chain is fixed to the D-shaped bracket, which has a chain track adapted to wrap the chain along the periphery of the bracket. Thus, as the pedal is depressed, the D-shaped bracket pulls the chain down and forward. The pulling action on the chain is converted by a power transfer assembly into a rotation of the rear wheel. The power transfer assembly includes a shaft journalled for unidirectional rotation on support plates. A sprocket is fixed to the shaft and carries a chain that drives rear wheel. Clutches are mounted on the shaft, and a length of pull chain, for example, runs over a pulley associated with the clutch. A pair of coil springs are used to restore the pedals to their upper position. The coil springs are mounted around clutches and fixed against rotation by locating a hooking end about the frame shaft. One coil spring is tensioned as a pedal is depressed and chain is pulled. When the pedal is released, the coil spring then draws the chain back, restoring the pedal.
U.S. Pat. No. 6,749,211 to Yliniemi discloses a bicycle in which stepping on pedals rotates a front wheel. The bicycle has a force converting mechanism that includes a line consisting of a near vertical length of spring, an intermediate length of chain wrapped around a forward wheel sprocket, and a length of cable that travels over a pulley and fastens to an upper end of a pedal. The spring assists in keeping the line taut and in restoring the pedal to an upper position.
Canadian patent application no. 2,296,166 to one of the inventors of the present invention was laid open for public inspection on Jul. 17, 2001. The prior patent application describes a stepper bicycle whose general features have been adopted for implementation of the present invention. The bicycle has a frame to which forward and rear wheels are mounted, and a steering wheel coupled to the forward wheel. A drive sprocket is fixed to an axle which is mounted for rotation on the frame, and an endless chain couples the drive sprocket to a rear wheel sprocket to apply torque to the rear wheel. The bicycle comprises a pair of elongate pedals positioned one to either side of the frame, and extending rearward from a pivot connection at a forward section of the frame. Each pedal comprises an apertured member formed with a large opening. The axle has a pair of crank arms, and each crank arm has a horizontal member that extends into a different one of the openings defined by apertured members. As the rider steps on each pedal, downward pivoting of the pedal effectively applies a torque to the drive sprocket which in turn applies a torque to the rear wheel. An object of the invention is to improve the efficiency of such a bicycle and to provide smoother operation.